/*-------------------------------------------------------------------------
 *
 * rewriteHandler.c--
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    $Header: /usr/local/cvsroot/postgres95/src/backend/rewrite/rewriteHandler.c,v 1.2 1996/11/24 05:58:57 bryanh Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
#include "miscadmin.h"
#include "utils/palloc.h"
#include "utils/elog.h"
#include "utils/rel.h"
#include "nodes/pg_list.h"	
#include "nodes/primnodes.h"

#include "parser/parsetree.h"		/* for parsetree manipulation */
#include "nodes/parsenodes.h"

#include "rewrite/rewriteSupport.h"	
#include "rewrite/rewriteHandler.h"
#include "rewrite/rewriteManip.h"
#include "rewrite/locks.h"

#include "commands/creatinh.h"
#include "access/heapam.h"

static void ApplyRetrieveRule(Query *parsetree, RewriteRule *rule, 
			      int rt_index, int relation_level, int *modified);
static List *fireRules(Query *parsetree, int rt_index, CmdType event,
		       bool *instead_flag, List *locks, List **qual_products);
static List *deepRewriteQuery(Query *parsetree);

/*
 * gatherRewriteMeta -
 *    Gather meta information about parsetree, and rule. Fix rule body
 *    and qualifier so that they can be mixed with the parsetree and
 *    maintain semantic validity
 */
static RewriteInfo *
gatherRewriteMeta(Query *parsetree,
		  Query *rule_action,
		  Node *rule_qual,
		  int rt_index,
		  CmdType event,
		  bool *instead_flag)
{
    RewriteInfo *info;    
    int rt_length;
    int result_reln;
    
    info = (RewriteInfo *) palloc(sizeof(RewriteInfo));
    info->rt_index = rt_index;
    info->event = event;
    info->instead_flag = *instead_flag;
    info->rule_action = (Query*)copyObject(rule_action);
    info->rule_qual = (Node*)copyObject(rule_qual);
    if (info->rule_action == NULL) info->nothing = TRUE;
    else {
        info->nothing = FALSE;
        info->action = info->rule_action->commandType;
        info->current_varno = rt_index;
        info->rt = parsetree->rtable;
        rt_length = length(info->rt);
        info->rt = append(info->rt, info->rule_action->rtable); 

        info->new_varno = PRS2_NEW_VARNO + rt_length;
        OffsetVarNodes(info->rule_action->qual, rt_length);
        OffsetVarNodes((Node*)info->rule_action->targetList, rt_length);
        OffsetVarNodes(info->rule_qual, rt_length);
        ChangeVarNodes((Node*)info->rule_action->qual,
                       PRS2_CURRENT_VARNO+rt_length, rt_index);
        ChangeVarNodes((Node*)info->rule_action->targetList,
                       PRS2_CURRENT_VARNO+rt_length, rt_index);
        ChangeVarNodes(info->rule_qual, 
                       PRS2_CURRENT_VARNO+rt_length, rt_index);

        /*
         * bug here about replace CURRENT  -- sort of
         * replace current is deprecated now so this code shouldn't really
         * need to be so clutzy but.....
         */
        if (info->action != CMD_SELECT) {	/* i.e update XXXXX */
            int new_result_reln = 0;
            result_reln = info->rule_action->resultRelation;
            switch (result_reln) {
              case PRS2_CURRENT_VARNO: new_result_reln = rt_index;
                break; 
              case PRS2_NEW_VARNO:	/* XXX */
              default:
                new_result_reln = result_reln + rt_length;
                break;
            }
            info->rule_action->resultRelation = new_result_reln;
        }
    }
    return info;
}

static List *
OptimizeRIRRules(List *locks)
{
    List *attr_level = NIL, *i;
    List *relation_level = NIL;
    
    foreach (i, locks) {
	RewriteRule *rule_lock 	= lfirst(i);

	if (rule_lock->attrno == -1) 
	    relation_level = lappend(relation_level, rule_lock);
	else
	    attr_level = lappend(attr_level, rule_lock);
    }
    return nconc(relation_level, attr_level);
}

/*
 * idea is to put instead rules before regular rules so that
 * excess semantically queasy queries aren't processed
 */
static List *
orderRules(List *locks)
{
    List *regular = NIL, *i;
    List *instead_rules = NIL;
    
    foreach (i, locks) {
	RewriteRule *rule_lock 	= (RewriteRule *)lfirst(i);

	if (rule_lock->isInstead)
	    instead_rules = lappend(instead_rules, rule_lock);
	else
	    regular = lappend(regular, rule_lock);
    }
    return nconc(regular, instead_rules);
}

static int
AllRetrieve(List *actions)
{
    List *n;
    
    foreach(n, actions) {
        Query *pt = lfirst(n);

	/*
	 * in the old postgres code, we check whether command_type is
	 * a consp of '('*'.commandType). but we've never supported transitive
	 * closures. Hence removed    - ay 10/94.
	 */
	if (pt->commandType != CMD_SELECT)
	    return false;
    }
    return true;
}

static List *
FireRetrieveRulesAtQuery(Query *parsetree,
			 int rt_index,
			 Relation relation,
			 bool *instead_flag,
			 int rule_flag)
{
    List *i, *locks;
    RuleLock *rt_entry_locks = NULL;
    List *work = NIL;

    if ((rt_entry_locks = relation->rd_rules) == NULL)
	return NIL;
    
    locks = matchLocks(CMD_SELECT, rt_entry_locks, rt_index, parsetree);

    /* find all retrieve instead */
    foreach (i, locks) {
	RewriteRule *rule_lock 	= (RewriteRule *)lfirst(i);
	
	if (!rule_lock->isInstead)
	    continue;
	work = lappend(work, rule_lock);
    }
    if (work != NIL) {
	work = OptimizeRIRRules(locks);
	foreach (i, work) {
	    RewriteRule *rule_lock = lfirst(i);
	    int relation_level;
	    int modified = FALSE;

	    relation_level = (rule_lock->attrno == -1);
	    if (rule_lock->actions == NIL) {
		*instead_flag = TRUE;
		return NIL;
	    }
	    if (!rule_flag &&
		length(rule_lock->actions) >= 2 &&
		AllRetrieve(rule_lock->actions)) {
		*instead_flag = TRUE;
		return rule_lock->actions;
	    }
	    ApplyRetrieveRule(parsetree, rule_lock, rt_index, relation_level,
			      &modified);
	    if (modified) {
		*instead_flag = TRUE;
		FixResdomTypes(parsetree->targetList);
		return lcons(parsetree,NIL);
	    }
	}
    }
    return NIL;
}	


/* Idea is like this:
 *
 * retrieve-instead-retrieve rules have different semantics than update nodes
 * Separate RIR rules from others.  Pass others to FireRules.
 * Order RIR rules and process.
 *
 * side effect: parsetree's rtable field might be changed
 */
static void
ApplyRetrieveRule(Query *parsetree,
		  RewriteRule *rule, 
		  int rt_index,
		  int relation_level,
		  int *modified)
{
    Query *rule_action = NULL;
    Node *rule_qual;
    List *rtable, *rt;
    int nothing, rt_length;
    int badsql= FALSE;

    rule_qual = rule->qual;
    if (rule->actions) {
	if (length(rule->actions) > 1)	/* ??? because we don't handle rules
					   with more than one action? -ay */
	    return;
	rule_action = copyObject(lfirst(rule->actions));
	nothing = FALSE;
    } else {
	nothing = TRUE;
    }

    rtable = copyObject(parsetree->rtable);
    foreach (rt, rtable) {
	RangeTblEntry *rte = lfirst(rt);
	/*
	 * this is to prevent add_missing_vars_to_base_rels() from
	 * adding a bogus entry to the new target list.
	 */
	rte->inFromCl = false;
    }
    rt_length = length(rtable);
    rtable = nconc(rtable, copyObject(rule_action->rtable)); 
    parsetree->rtable = rtable;

    rule_action->rtable = rtable;
    OffsetVarNodes(rule_action->qual, rt_length);
    OffsetVarNodes((Node*)rule_action->targetList, rt_length);
    OffsetVarNodes(rule_qual, rt_length);
    ChangeVarNodes(rule_action->qual,
		   PRS2_CURRENT_VARNO+rt_length, rt_index);
    ChangeVarNodes((Node*)rule_action->targetList,
		   PRS2_CURRENT_VARNO+rt_length, rt_index);
    ChangeVarNodes(rule_qual, PRS2_CURRENT_VARNO+rt_length, rt_index);
    if (relation_level) {
	HandleViewRule(parsetree, rtable, rule_action->targetList, rt_index,
		       modified);
    } else {
	HandleRIRAttributeRule(parsetree, rtable, rule_action->targetList,
			       rt_index, rule->attrno, modified, &badsql);
    }
    if (*modified && !badsql)
	AddQual(parsetree, rule_action->qual);
}

static List *
ProcessRetrieveQuery(Query *parsetree,
		     List *rtable,
		     bool *instead_flag,
		     bool rule)
{
    List *rt;
    List *product_queries = NIL;
    int rt_index = 0;
    
    foreach (rt, rtable) {
	RangeTblEntry *rt_entry = lfirst(rt);
	Relation rt_entry_relation = NULL;
	List *result = NIL;
	
	rt_index++;
	rt_entry_relation = heap_openr(rt_entry->relname);

	if (rt_entry_relation->rd_rules != NULL) {
	    result = 
		FireRetrieveRulesAtQuery(parsetree,
					 rt_index,
					 rt_entry_relation,
					 instead_flag,
					 rule);
	}
	heap_close(rt_entry_relation);
	if (*instead_flag)
	    return result;
    }
    if (rule)
	return NIL;

    foreach (rt, rtable) {
	RangeTblEntry *rt_entry = lfirst(rt);
	Relation rt_entry_relation = NULL;
	RuleLock *rt_entry_locks = NULL;
	List *result = NIL;
	List *locks = NIL;
	List *dummy_products;

	rt_index++;
	rt_entry_relation = heap_openr(rt_entry->relname);
	rt_entry_locks = rt_entry_relation->rd_rules;
	heap_close(rt_entry_relation);

	if (rt_entry_locks) {
	    locks =
		matchLocks(CMD_SELECT, rt_entry_locks, rt_index, parsetree);
	}
	if (locks != NIL) {
	    result = fireRules(parsetree, rt_index, CMD_SELECT,
			       instead_flag, locks, &dummy_products);
	    if (*instead_flag)
		return lappend(NIL, result);
	    if (result != NIL)
		product_queries = nconc(product_queries, result);
	}
    }
    return product_queries;
}

static Query *
CopyAndAddQual(Query *parsetree,
	       List *actions,
	       Node *rule_qual,
	       int rt_index,
	       CmdType event)
{
    Query *new_tree = (Query *) copyObject(parsetree);
    Node *new_qual = NULL;
    Query *rule_action = NULL;
    
    if (actions)
	rule_action = lfirst(actions);
    if (rule_qual != NULL)
	new_qual = (Node *)copyObject(rule_qual);
    if (rule_action != NULL) {
	List *rtable;
	int rt_length;
	
	rtable = new_tree->rtable;
	rt_length = length(rtable);
	rtable = append(rtable,listCopy(rule_action->rtable));
	new_tree->rtable = rtable;
	OffsetVarNodes(new_qual, rt_length);
	ChangeVarNodes(new_qual, PRS2_CURRENT_VARNO+rt_length, rt_index);
    }
    /* XXX -- where current doesn't work for instead nothing.... yet*/
    AddNotQual(new_tree, new_qual);

    return new_tree;
}


/*
 *  fireRules -
 *     Iterate through rule locks applying rules.  After an instead rule
 *     rule has been applied, return just new parsetree and let RewriteQuery
 *     start the process all over again.  The locks are reordered to maintain
 *     sensible semantics.  remember: reality is for dead birds -- glass
 *
 */
static List *
fireRules(Query *parsetree,
	  int rt_index,
	  CmdType event,
	  bool *instead_flag,
	  List *locks,
	  List **qual_products)
{
    RewriteInfo *info;
    List *results = NIL;
    List *i;
    
    /* choose rule to fire from list of rules */
    if (locks == NIL) {
	(void) ProcessRetrieveQuery(parsetree,
				    parsetree->rtable,
				    instead_flag, TRUE);
	if (*instead_flag)
	    return lappend(NIL, parsetree);
	else
	    return NIL;
    }
    
    locks = orderRules(locks);	/* instead rules first */
    foreach (i, locks) {
	RewriteRule *rule_lock = (RewriteRule *)lfirst(i);
	Node *qual, *event_qual;
	List *actions;
	List *r;
	bool orig_instead_flag = *instead_flag;

	/* multiple rule action time */
	*instead_flag = rule_lock->isInstead;
	event_qual = rule_lock->qual;
	actions = rule_lock->actions;
	if (event_qual != NULL && *instead_flag)
	    *qual_products =
		lappend(*qual_products,
			 CopyAndAddQual(parsetree, actions, event_qual,
					rt_index, event));
	foreach (r, actions) {
	    Query *rule_action  = lfirst(r);
	    Node *rule_qual = copyObject(event_qual);
	    
	    /*--------------------------------------------------
	     * Step 1:
	     *    Rewrite current.attribute or current to tuple variable
	     *    this appears to be done in parser?
	     *--------------------------------------------------
	     */
	    info = gatherRewriteMeta(parsetree, rule_action, rule_qual,
				     rt_index,event,instead_flag);
	    
	    /* handle escapable cases, or those handled by other code */
	    if (info->nothing) {
		if (*instead_flag)
		    return NIL;
		else
		    continue;
	    }

	    if (info->action == info->event &&
		info->event == CMD_SELECT)
		continue;

	    /*
	     * Event Qualification forces copying of parsetree --- XXX
	     * and splitting into two queries one w/rule_qual, one
	     * w/NOT rule_qual. Also add user query qual onto rule action
	     */
	    qual = parsetree->qual;
	    AddQual(info->rule_action, qual);
	    
	    if (info->rule_qual != NULL)
		AddQual(info->rule_action, info->rule_qual);
	    
	    /*--------------------------------------------------
	     * Step 2:
	     *    Rewrite new.attribute w/ right hand side of target-list
	     *    entry for appropriate field name in insert/update
	     *--------------------------------------------------
	     */  
	    if ((info->event == CMD_INSERT) || (info->event == CMD_UPDATE)) {
		FixNew(info, parsetree);
	    }
	    
	    /*--------------------------------------------------
	     * Step 3:
	     *    rewriting due to retrieve rules 
	     *--------------------------------------------------
	     */
	    info->rule_action->rtable = info->rt;       	   
	    (void) ProcessRetrieveQuery(info->rule_action, info->rt,
					&orig_instead_flag, TRUE);
	    
	    /*--------------------------------------------------  
	     * Step 4
	     *    Simplify? hey, no algorithm for simplification... let
	     *    the planner do it.
	     *--------------------------------------------------  
	     */
	    results = lappend(results, info->rule_action);

	    pfree(info);
	}
	if (*instead_flag) break;
    }
    return results;
}

static List *
RewriteQuery(Query *parsetree, bool *instead_flag, List **qual_products)
{
    CmdType event;
    List *product_queries = NIL;
    int result_relation =  0;
    
    Assert(parsetree != NULL);
    
    event = parsetree->commandType;

    if (event == CMD_UTILITY)
	return NIL;

    /*
     * only for a delete may the targetlist be NULL
     */
    if (event != CMD_DELETE) {
 	Assert(parsetree->targetList != NULL);
    }
    
    result_relation = parsetree->resultRelation;

    if (event != CMD_SELECT) {
	/*
	 * the statement is an update, insert or delete
	 */
	RangeTblEntry *rt_entry;
	Relation rt_entry_relation = NULL;
	RuleLock *rt_entry_locks = NULL;
	
	rt_entry = rt_fetch(result_relation, parsetree->rtable);
	rt_entry_relation = heap_openr(rt_entry->relname);
	rt_entry_locks = rt_entry_relation->rd_rules;
	heap_close(rt_entry_relation);

	if (rt_entry_locks != NULL) {
	    List *locks =
		matchLocks(event, rt_entry_locks, result_relation, parsetree);
	    
	    product_queries =
		fireRules(parsetree, 
			  result_relation,
			  event,
			  instead_flag,
			  locks,
			  qual_products);
	}
	return product_queries;
    }else {
	/*
	 * the statement is a select
	 */
	Query *other;

	other = copyObject(parsetree);	/* ApplyRetrieveRule changes the
					   range table */
	return
	    ProcessRetrieveQuery(other, parsetree->rtable,
				 instead_flag, FALSE);
    }
}

/*
 * to avoid infinite recursion, we restrict the number of times a query
 * can be rewritten. Detecting cycles is left for the reader as an excercise.
 */
#ifndef REWRITE_INVOKE_MAX
#define REWRITE_INVOKE_MAX	10
#endif

static int numQueryRewriteInvoked = 0;

/*
 * QueryRewrite -
 *    rewrite one query via QueryRewrite system, possibly returning 0, or many
 *    queries
 */  
List *
QueryRewrite(Query *parsetree)
{
    numQueryRewriteInvoked = 0;

    /*
     * take a deep breath and apply all the rewrite rules - ay
     */
    return deepRewriteQuery(parsetree);
}

/*
 * deepRewriteQuery -
 *    rewrites the query and apply the rules again on the queries rewritten
 */
static List *
deepRewriteQuery(Query *parsetree)
{
    List *n;
    List *rewritten = NIL;
    List *result = NIL;
    bool instead;
    List *qual_products = NIL;

    if (++numQueryRewriteInvoked > REWRITE_INVOKE_MAX) {
	elog(WARN, "query rewritten %d times, may contain cycles",
	     numQueryRewriteInvoked-1);
    }
    
    instead = FALSE;
    result = RewriteQuery(parsetree, &instead, &qual_products);
    if (!instead)
	rewritten = lcons(parsetree, NIL);

    foreach(n, result) {
        Query *pt = lfirst(n);
        List *newstuff = NIL;
	
        newstuff = deepRewriteQuery(pt);
        if (newstuff != NIL)
	    rewritten = nconc(rewritten, newstuff);
    }
    if (qual_products != NIL)
	rewritten = nconc(rewritten, qual_products);

    return rewritten;
}

